Transient tyre characteristic

[marcush.]

the knowledge and expertise exposed by some of our forum members is appreciated and from my side I´m glad to have the chance to get that much insight putting my handson only experience into some context.
Many thanks .

[Krispy]

I am in no way a tire engineer, nor do I claim to be, however I have spent some time looking at Lateral force vs. slip angle graphs and have noticed a difference between bias ply and radial tyres. Mind you this isn't transient behaviour but since there is a difference I have noticed I wanted to poll the "experts" JT, Ben, Speedsense.

Is it possible to generalize a bias ply tire as more forgiving? Looking at the Fy vs Alpha graps there is a larger plateu (larger range of slip angles that result in a high lateral force)on bias ply tyres than on radials?

Edit: Add Transient Stuff

Also, I did some testing a while back of bias ply to radial tyres based around response time after a drivers "step" input to the wheel and found the bias ply tyres to be slower but favored by most drivers.

[Jersey Tom]

The thing is.. it's a little silly to call a tire "bias" or "radial" like it's a binary, one-or-the-other classification. Just as silly as broadly calling a car "understeer" or "oversteer," or that one driver likes one or the other. It's a sliding scale. You can have ply angles of 90 degrees (totally radial), you can have ply angles of 45 degrees, or anywhere in between.

Belted versus not-belted might be a better binary attribute.

With regard to transients... especially on a car when doing step steers and such... there are two or three things that you have to sort out.

1) Needs to be at a constant, controlled speed.. since the change in yaw damping with forward velocity will dramatically change responsiveness

2) The biggest player will probably be the steady state lateral force gain (cornering stiffness). Tires with higher cornering stiffness -> better transient response.

3) Then there's the true transient tire response. How much of an influence it is.. really depends on the application.

[bill shoe]

ben, it's great that you have gainful employment but that's not really impressive here. I've had several high level interactions with speedsense on this forum and learned useful things from him. If you had useful knowledge and the ability to communicate it then you'd also be adding to this thread instead of throwing angry little negative-energy bombs.

[bill shoe]

And Jersey Tom, i'm going to disagree with you in a more respectful way. You and other "tire insiders" are trying to have your cake and eat it too. Your company puts out two different kinds of tires and your company calls them "A" and "B". Then a consumer of those products refers to them as "A" and "B". Then you tell the consumer he does not really know what he's talking about because A and B are not really A and B.

It is true that "A" and "B" may not be the most hard-ass technically accurate description possible. However, this discrepency does not make you technically sophisticated, it just means your company is crappy with naming and communicating about their products.

My perspective as a tire insider.

[DaveW]

Back on topic, perhaps. Google "First Order Tyre (or Tire) Dynamics" to find an interesting paper by Georg Rill.

[Jersey Tom]

And Jersey Tom, i'm going to disagree with you in a more respectful way. You and other "tire insiders" are trying to have your cake and eat it too. Your company puts out two different kinds of tires and your company calls them "A" and "B". Then a consumer of those products refers to them as "A" and "B". Then you tell the consumer he does not really know what he's talking about because A and B are not really A and B.

Eh, kinda.

There is a binary difference between "bias" and "radial" tires, but it's a manufacturing difference. That's what leads to the stamping on the sidewall.

But for the sake of this discussion where we're talking about performance characteristics, the ply angle is a sliding scale.

In any event, I wouldn't be comfortable saying that generally A is 'edgy' and B is 'forgiving' since I've seen plenty of tires on both extremes of the spectrum which can exhibit smooth or violent breakaway.

Even in performance consumer tire markets which are much closer to the "radial" end of the range, some tires are very crisp, precise, and smooth... whereas others can be lazy, non-linear, and abrupt in breakaway.

[ubrben]

ben, it's great that you have gainful employment but that's not really impressive here. I've had several high level interactions with speedsense on this forum and learned useful things from him. If you had useful knowledge and the ability to communicate it then you'd also be adding to this thread instead of throwing angry little negative-energy bombs.

I don't doubt that. All I said was that his first post was sufficiently lacking is specifics to make any useful points. It boiled down to two tyres can be different and different drivers will prefer different tyres. With all due respect that's stating the obvious but doesn't tell us much about transient tyre characteristics.

Your right, I've got very little data on tyre transients, but my experience is similar to JT's that lateral force gain (cornering stiffness) seems to be more important than relaxation length.

I totally agree with your subsequent point that tyre companies want to have their cake and eat it. Frustrates me every day. We moan that people have funny ideas about tyres and then give them no info to form a decent opinion.

Ben

[DaveW]

Your right, I've got very little data on tyre transients, but my experience is similar to JT's that lateral force gain (cornering stiffness) seems to be more important than relaxation length.

Ben, the Rill paper I referred to previously suggests there is a relationship between cornering stiffness & relaxation length, if I understand you (& Rill) correctly. See equations 13 & 14.

[Jersey Tom]

In a very simple relaxation length approximation, cornering stiffness is part of it, yes.

[ubrben]

First order it's related to lateral stiffness and cornering stiffness. In my experience the transient response of the tyre is so fast that control moment tends to dominate the driver's opinion on the response of the car as a whole.

Ben

[DaveW]

In my experience the transient response of the tyre is so fast that control moment tends to dominate the driver's opinion on the response of the car as a whole.

I would like to agree with you (& certainly work under that assumption). It doesn't stop damper people trying to sell "magic", however. Have you heard of the Ohlins patented "high frequency function piston" which, according to the blurb, "gives a short, low dampened stroke" (aka "backlash", so far as I have been able to "see")?

Interestingly, perhaps, I first heard about the phenomenon a (long) time ago, when John Miles introduced backlash in a set of front dampers by accident, and "transformed" the handling characteristics of a racing Esprit he was working on. It was he, BTW, that talked about tyres "buckling".

Having said all that, I believe firmly that backlash (accidental or deliberate) is not the correct solution.

[speedsense]

The thing is.. it's a little silly to call a tire "bias" or "radial" like it's a binary, one-or-the-other classification. Just as silly as broadly calling a car "understeer" or "oversteer," or that one driver likes one or the other. It's a sliding scale. You can have ply angles of 90 degrees (totally radial), you can have ply angles of 45 degrees, or anywhere in between.

Belted versus not-belted might be a better binary attribute.

Then the sales/engineers that work for the tire companies,and the tire company itself are silly because they still represent their tire choices as bias or radial. By your words they are lying to us and still stamp their tires as such. If it's meanlingless, then to the racing public it's a huge con job.

I doubt that very much, by the way.

One simple test proves out that there's more than a slight difference- inflating a racing "radial" to 45 pounds and measuring statically the crown and the vertical spring rate. The "radial" will crown only slightly (less than 1/8") and if I heat it in a tire blanket at say, 220 for 8 hours @ 45 psi, the tire will change it's diameter (grow) only slightly when returned to it's original running pressure. Do the same thing to a "bias ply" racing tire and two things will happen, the tire will crown largely at 45 psi, over it's radial counterpart and heating it the same way will cause a "growth" in diameter unlike the "radial". Binary and two very different tires. (BTW, this test has been performed on more than one tire manufacturer)
And to add this difference, the "radial" can run on the race track at 45 psi and not explode (even when the tire company says not to go above 29 psi). The bias either would explode, overheat or can't be driven at such a pressure.

Three examples of tires that are labeled radial and bias, neither reacts in the same way. Yet you claim the differences are small ones and blurred by the names bias and radial.

[Jersey Tom]

No, I just think way too broad assumptions and classifications are being made here... and that the differences don't come down to ply angle as in the textbook definition of a radial.

Honestly, like I said, the biggest difference is how they're physically put together on the build machines. That is a binary attribute. Are race "radials" typically going to have higher ply angles than bias slicks? Sure. But often they literally do not fit the definition of a radial ply tire.

In any event, we can go down the road of nit picking and intellectual masturbation for hours. I just don't like the broad categorization.

I can have two "bias" tires and one will be very susceptible to high-temperature creep whereas the other will hardly move.

I can have a radial and bias of (almost) the same size... and I can have either one of them have more response and "lateral" stiffness feel (cornering stiffness, etc) than the other. Both radial and bias tires can be smooth, predictable, and controllable at the limit.. or a complete trainwreck.

So to the earlier point in this thread, I just would not be comfortable saying "radials fundamentally behave like this, and bias behave like that." Lots of area for crossover. Not to mention, as I said, that I can have a control construction and two different compounds.. providing very close levels of grip.. but driving completely differently.

You can cite a handful of examples that are "black and white," but in my opinion and experience, at the "big picture" level it is very gray.

[speedsense]

No, I just think way too broad assumptions and classifications are being made here... and that the differences don't come down to ply angle as in the textbook definition of a radial.

Honestly, like I said, the biggest difference is how they're physically put together on the build machines. That is a binary attribute. Are race "radials" typically going to have higher ply angles than bias slicks? Sure. But often they literally do not fit the definition of a radial ply tire.

In any event, we can go down the road of nit picking and intellectual masturbation for hours. I just don't like the broad categorization.

I can have two "bias" tires and one will be very susceptible to high-temperature creep whereas the other will hardly move.

I can have a radial and bias of (almost) the same size... and I can have either one of them have more response and "lateral" stiffness feel (cornering stiffness, etc) than the other. Both radial and bias tires can be smooth, predictable, and controllable at the limit.. or a complete trainwreck.

So to the earlier point in this thread, I just would not be comfortable saying "radials fundamentally behave like this, and bias behave like that." Lots of area for crossover. Not to mention, as I said, that I can have a control construction and two different compounds.. providing very close levels of grip.. but driving completely differently.

You can cite a handful of examples that are "black and white," but in my opinion and experience, at the "big picture" level it is very gray.

I can quite a few examples related to an entire series,
1990 Formula Atlantic, switched from (goodyear bias to Yokohama radials)
1993 Pro FF2000 switched from bias to radials
1993 Olds Pro (S2000) switched from bias to radials
1997 (96?) Trans Am switched from bias to radials
2003 Formula Mazda switched cars and tires from bias to radials


In every single instance, the drivers who had aggressive driving techniques and where consistent at running at the front on bias, suddenly found themselves down the order unless their technique changed to a "smoother" style. Entry and exit "approaches" where greatly effected and demanded a smoother driving style.

Tell Claude Bourbonnais (whom I regard as one the fastest drivers ever in America/Canada) who was faster on a regular basis than Jacques Villeneuve,when they were team mates a few years later, that the difference between bias and radials is a "gray" area. Claude greatly struggled with radials until he adapted his driving technique.
Many of the driver's struggled in each of these series with the switch, if their technique was what I consider aggressive,high rotation, on the "edge" car control technique and until they calmed it down to a smoother entry, exit technique, they remained uncompetitive to the already smoother driver that started running at the front.

BTW, I was working in each one of these series when this occurred, so it's firsthand experience and there was nothing gray about it. An observation yes, but an observation based in data acquisiton, the numbers don't lie and driver's can't ....

Maybe the biggest difference in thread is perception, as my perception is directly from debriefing a driver and analyzing data directly from the car, so I hear it first hand. The tire engineers only hear what an engineer/crew chief is "wiiling" to relate to them and very rarely (if ever) are the tire guys speaking directly to the driver for their opinion on a set of tires.

Driver's can tell you all day long how different the two types of tires are. And the tire companies can tell me all day how little difference there is. Guess who I'm going to believe.

IMHO